1. Field of the Invention
The present invention relates to a pigment powder having high conductivity and improved color tone, and a transparent conductive film formed on the outer surface of a transparent substrate (face panel) of a cathode ray tube by using the conductive pigment powder and having an anti-reflection function and a leakage electric field preventing function.
2. Discussion of the Background
On the other hand, in cathode ray tubes such as TV Braun tubes and computer CRT, there has recently been concern that leakage of electromagnetic waves from a portion near an electron gun and a deflecting yoke provided therein adversely affects peripheral electronic apparatus and the human body. In order to prevent leakage of electromagnetic waves (electric field), it is necessary to form a conductive film on the outer surface of the face panel of the cathode ray tube to decrease the surface resistance value. When a conductive film includes metal fine particles or a metal compound fine particles and is a thin film, the conductive film generally absorbs visible light. Making the film thicker to decrease the resistance value deteriorates light transmittance, and the luminance of a cathode ray tube deteriorates as a result.
In order to solve this problem, a transparent conductive film has been proposed, which is formed by coating a transparent conductive film forming composition containing a conductive fine powder, a solvent and a non-polymeric film forming agent containing no polymeric binder on a base material, impregnating the coated film on the base material with a solution having viscosity of 25 cps or less and containing a polymeric binder, and then drying or curing the coated film (Japanese Unexamined Patent Publication No. 8-102227). In the transparent conductive film, the conductive fine powder is a fine powder of indium oxide containing tin.
The thus-formed transparent conductive film has a surface resistivity of 1xc3x97105xcexa9 or less and haze (the ratio of the diffused transmitted light to direct transmitted light) as low as 1% or less, and thus has a high level of conductivity required for electromagnetic shield, causing no deterioration in luminance of the cathode ray tube. The transparent conductive film also has the property that adhesion to a base material, and film strength are increased.
The present inventors applied for a patent of a low-resistance conductive pigment that contains an indium oxide crystal containing tin, wherein the tin content is 1 to 15 mol % based on the total amount of indium and tin, the surface acidity is 8xc3x9710xe2x88x927 to 1xc3x9710xe2x88x925 mol/m2, and the volume resistivity of a 5-MPa green compact measured by a four-probe method is less than 2xc3x97100 xcexa9xc2x7cm and not less than 2xc3x9710xe2x88x922 xcexa9xc2x7cm. (Japanese Unexamined Patent Publication No. 6-247716).
The low-resistance conductive pigment described above is a bluish pigment having lower resistance than a conventional pigment with tin-containing indium oxide, and permits the formation of a transparent conductive film having excellent visibility.
However, the conventional low-resistance conductive pigment disclosed in Japanese Unexamined Patent Publication No. 6-247716 is a bluish conductive pigment and has high volume resistivity, and thus a conductive pigment having an improved purple tone and low volume resistivity is required.
Although dioxazine violet is known as a pigment having a purple tone, this pigment has a problem in that the volume resistivity is as high as about 1xc3x971010 xcexa9xc2x7cm.
On the other hand, the transparent conductive film disclosed in Japanese Unexamined Patent Publication No. 8-102227 has a defect that it cannot be burned unless the temperature is as relatively high as 400 to 500xc2x0 C.
The transparent conductive film further has a problem in which the surface resistance value of the transparent conductive film changes with time, i.e., the surface resistivity increases with the passage of time.
There is also a demand for a transparent conductive film which can be burned at a lower temperature and has lower surface resistivity.
A first object of the present invention is to provide a conductive pigment powder having an improved color tone and a low volume resistivity of 5-MPa green compact.
A second object of the present invention is to provide a conductive pigment powder permitting the formation of a transparent conductive film having excellent visibility.
A third object of the present invention is to provide a transparent conductive film having high adhesion to a transparent substrate (face panel) and film strength, and permitting surface resistivity to be decreased by burning at a relatively low temperature and the prevention of change in the surface resistance with time.
These and other objects have now been attained by the present invention, the first embodiment of which provides a conductive pigment powder, which includes indium oxide, tin and gold, and having a purple color tone.
Another embodiment of the present invention provides a method of producing a conductive pigment powder, which includes:
coprecipitating one or more hydroxides by reacting a mixed aqueous solution that includes an indium salt, a tin salt and a gold salt, with an alkaline aqueous solution, to obtain one or more hydroxides; and
heating the hydroxides.
Another embodiment of the present invention provides a dispersion solution, which includes the above-mentioned conductive pigment powder dispersed in one or both of an organic solvent and water, wherein the content of the powder in the solution is 0.01 to 90% by weight.
Another embodiment of the present invention provides a transparent conductive film, which includes the above-mentioned conductive pigment powder.
Another embodiment of the present invention provides a method of forming a transparent conductive film, which includes:
mixing an aqueous solution that includes indium ions, an aqueous solution that includes tin ions, and an aqueous solution that includes gold ions, to form a mixture;
reacting the mixture with an alkaline aqueous solution to form at least one coprecipitated hydroxide;
heating the coprecipitated hydroxide at 350 to 1100xc2x0 C. to form a conductive pigment powder;
mixing the conductive pigment powder with a solvent that includes one or both of an organic solvent and water, to form a dispersion solution;
coating the dispersion solution on a transparent substrate to form a deposited film; and
burning the deposited film at a predetermined temperature to form a transparent conductive film.
Another embodiment of the present invention provides a cathode ray tube, which includes the above-mentioned transparent conductive film and a transparent substrate, wherein the transparent conductive film is formed on an outer surface of the transparent substrate.